Dynamic random access memory (DRAM) may be accessed via an asynchronous interface or a synchronous interface. Synchronous dynamic random access memory (SDRAM) is DRAM that is accessed via a synchronous interface, such as a double data rate (DDR) interface. Mobile DDR (mDDR), which is sometimes referred to as Low Power DDR (LPDDR), is a type of SDRAM for mobile devices. Like SDRAM generally, mDDR is accessed via a synchronous interface, such as a DDR interface.
Static random-access memory (SRAM) is a type of semiconductor memory that uses bistable latching circuitry to store each bit. SRAM is considered static in that SRAM maintains values stored in it as long as it is powered. In contrast, in order for DRAM to maintain state, DRAM is periodically refreshed. SRAM may still be considered volatile because data is eventually lost when the memory is not powered. SRAM is generally more expensive than DRAM, but does not require refresh circuitry.
Non-volatile solid state memory may be memory that retains stored values even when power is disconnected from the non-volatile solid state memory. The non-volatile solid state memory may be flash memory, for example. Non-volatile solid state memory is typically accessed with a block storage protocol. For example, the block storage protocol may be a data access protocol that complies with a memory card standard for solid-state storage, such as MultiMediaCard (MMC), embedded card (eMMC), Secure Digital (SD), RS-MMC, MMCplus, MMCmobile, SecureMMC, SDIO SD, miniSD, and microSD. The non-volatile solid state memory may be accessed with the block storage protocol over a memory card bus that complies with the memory card standard.